Substituting large diameter, one-piece aluminum drive shafts for conventional two-piece steel constructions has become a popular means of reducing NVH (Noise, Vibration, and Harshness), cost, and weight in passenger car and light truck drive lines. In order to make use of common yokes or end fitting configurations, tubes ends are generally reduced in size via swaging to an inside diameter that appropriately matches the end fittings' mating surface.
A conventional system for reducing a tube end using a swaging process is illustrated in FIGS. 1(a)-1(c). Generally, a tube 10 is interconnected to a clamp 20, which fixedly positions the tube 10 in a predetermined orientation, as illustrated in FIG. 1(a). A push point swage die 30, having a swaging diameter 32 less than a diameter 12 of the tube 10, is pushed onto an end of the tube 10, thereby compressing that portion of tube 10 to the diameter 32 of the swage die 30, as illustrated in FIG. 1(b). The swage die 30 is then removed from the tube 10 to provide a compressed end portion 14 of the tube 10 as illustrated in FIG. 1(c). The compressed end portion 14 generally has residual tensile stress, such as a tensile residual axial stress T1 and/or a tensile residual hoop stress T2.
In metal forming, “spring back” occurs after process defined deformation. The amount of spring back is a function of, among others, the material's dimensions, yield strength, tooling design, and degree of deformation as plotted against the respective material's stress strain curve. In the case of swaged drive shaft tubing, the diameter reduction may create tensile hoop and/or axial residual stress states, as illustrated above. In some cases, the degree of diameter reduction can impart a tensile residual stress state in the swaged portion that adversely effects weld quality, design interference fit, and the fatigue performance of the drive shaft.
Thermal techniques are known for treating wrought aluminum products having forming induced stress, such as those induced via swaging processes, but such thermal techniques are generally not effective in relieving stress without substantially reducing the mechanical properties of the material.